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Abstract:

An exemplary method includes positioning a lead in a patient where the
lead has a longitudinal axis that extends from a proximal end to a distal
end and where the lead includes an electrode with an electrical center
offset from the longitudinal axis of the lead body; measuring electrical
potential in a three-dimensional potential field using the electrode; and
based on the measuring and the offset of the electrical center,
determining lead roll about the longitudinal axis of the lead body where
lead roll may be used for correction of field heterogeneity, placement or
navigation of the lead or physiological monitoring (e.g., cardiac
function, respiration, etc.). Various other methods, devices, systems,
etc., are also disclosed.

Claims:

1.

32. A method comprising: positioning a lead in a patient wherein the lead
comprises a longitudinal axis that extends from a proximal end to a
distal end and wherein the lead comprises two or more electrodes, each
electrode having an electrical center offset from the longitudinal axis
of the lead body; measuring electrical potential in a three-dimensional
potential field using the two or more electrodes; and based on the
measuring and the offsets of the electrical centers, generating one or
more scaling factors to compensate for heterogeneity in the
three-dimensional potential field.

2. The method of claim 1 wherein the generating comprises providing
distances between the electrodes and an orientation for each electrical
center about the longitudinal axis of the lead body.

3. The method of claim 1 wherein the generating comprises determining a
position for each electrical center with respect to a coordinate system
of the three-dimensional potential field.

4. The method of claim 1 wherein the generating comprises determining a
position for each electrical center with respect to a local coordinate
system of the lead.

5. The method of claim 1 wherein the generating comprises determining a
position for each electrical center with respect to a local coordinate
system of the lead and determining a position for each electrical center
with respect to a coordinate system of the three-dimensional potential
field.

Description:

[0002] Subject matter presented herein relates generally to localization
systems and invasive therapies. Various examples pertain to lead-based
electrodes that can enhance lead localization for placement, navigation
or physiologic mapping. Such electrodes are optionally suited for
sensing, stimulation or sensing and stimulation.

BACKGROUND

[0003] Various techniques exist to "image" internal physiology. Some of
these techniques are considered "non-invasive", for example, those that
rely on penetration of sound (e.g., ultrasound), electromagnetic energy
(e.g., MRI, CT) or particles (e.g., PET). However, when such techniques
require enhancement, clinicians often resort to intravenous delivery of
contrast agents or dyes. For example, cardiac fluoroscopy can be enhanced
through use of contrast agents or dyes delivered intravenously via a
catheter. Further, fluoroscopy also provides some degree of
visualization, which can help a clinician navigate such a catheter in a
patient's body.

[0004] Another non-invasive technique is often referred to as "electrical
impedance tomography" or "electrical capacitance tomography". Such
techniques are referred to herein as simply "electrical tomography" (ET).
Conventional ET generates images of the body related to dielectric
properties and underlying physiology as reconstructed from skin-surface
electrical measurements. Typically, ET involves placing electrodes on the
skin and applying small alternating currents via some or all of the
electrodes. In turn, corresponding electrical potentials are measured and
processed to generate an image or images that represent the underlying
physiology.

[0005] An invasive variation of ET is referred to herein as ET
localization where one or more electrodes are introduced into the body
and relied upon for physiologic mapping or localization (e.g., via
delivery of electrical potentials or current, measurement of potentials
or current, etc.). A particular commercially available navigation and
localization system is marketed as the ENSITE® NAVX® system and
technology (St. Jude Medical, Inc., Minnesota).

[0006] In a typical clinical application, the ENSITE® NAVX® system
drives current across three pairs of body surface patches to create a
Cartesian coordinate system in the body, in which indwelling electrodes
may be located in real-time. Potentials sensed by the indwelling
electrodes in the current fields can be used to compute impedances that
determine a position of each electrode (e.g., in three dimensions). In
various clinical applications, indwelling electrodes may be used to
measure cardiac potentials and to deliver energy, for example to pace or
to ablate tissue. A computed position or positions of an indwelling
electrode or electrodes, in conjunction with the sensed electrograms and
possibly other information, can be used to generate maps that may include
anatomical features as well as information about tissue substrate and
performance.

[0007] Various exemplary technologies described herein pertain to
localization, navigation or both localization and navigation. Various
examples are described with respect to ET. As described in below, various
exemplary technologies may be optionally suited or adapted for use with
imaging modalities such as MR, CT and ultrasound (e.g., ultrasound
tomography, UT).

SUMMARY

[0008] An exemplary method includes positioning a lead in a patient where
the lead has a longitudinal axis that extends from a proximal end to a
distal end and where the lead includes an electrode with an electrical
center offset from the longitudinal axis of the lead body; measuring
electrical potential in a three-dimensional potential field using the
electrode; and based on the measuring and the offset of the electrical
center, determining lead roll about the longitudinal axis of the lead
body where lead roll may be used for correction of field heterogeneity,
placement or navigation of the lead or physiological monitoring (e.g.,
cardiac function, respiration, etc.). Various other methods, devices,
systems, etc., are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Features and advantages of the described implementations can be
more readily understood by reference to the following description taken
in conjunction with the accompanying drawings.

[0010] FIG. 1 is a simplified diagram illustrating an exemplary
implantable stimulation device in electrical communication with at least
three leads implanted into a patient's heart and at least one other lead
for sensing and/or delivering stimulation and/or shock therapy. Other
devices with more or fewer leads may also be suitable.

[0011] FIG. 2 is a functional block diagram of an exemplary implantable
stimulation device illustrating basic elements that are configured to
provide cardioversion, defibrillation, pacing stimulation and/or other
tissue stimulation. The implantable stimulation device is further
configured to sense information and administer therapy responsive to such
information.

[0012] FIG. 3 is a block diagram of an exemplary method for optimizing
therapy and/or monitoring conditions based at least in part on position
information.

[0013] FIG. 4 is an exemplary arrangement of a lead and electrodes for
acquiring position information and optionally other information.

[0014] FIG. 5 is a diagram illustrating field heterogeneities associated
with current generated fields in the body along with a method to
compensate for field heterogeneities.

[0015] FIG. 6 is a diagram illustrating a two lead scenario with respect
to a local coordinate system for each lead and a global coordinate
system.

[0016] FIG. 7 is a diagram of a conventional lead with symmetric roll in a
local coordinate system and an exemplary lead with asymmetric roll in a
local coordinate system as well as an exemplary method for using the
exemplary lead.

[0017] FIG. 8 is a diagram of an exemplary lead with twist tracking
features along with an exemplary method for using the exemplary lead.

[0018] FIG. 9 is a diagram of a conventional ring electrode and its
electrical center and a pair of exemplary electrodes and corresponding
individual electrical centers.

[0019] FIG. 10 is a series of diagrams illustrating various exemplary
electrodes with respect to a lead body.

[0020] FIG. 11 is a series of diagrams illustrating various exemplary
electrodes with respect to a lead body.

[0021] FIG. 12 is a series of diagrams illustrating various exemplary
electrodes with respect to a lead body.

[0022] FIG. 13 is a diagram of an exemplary localization system, exemplary
arrangement of leads in the heart and exemplary displays.

[0023] FIG. 14 is a diagram of an exemplary localization system, an
exemplary method and an exemplary sequence of data entry.

[0024] FIG. 15 is an exemplary system for acquiring information and
analyzing such information.

DETAILED DESCRIPTION

[0025] The following description includes the best mode presently
contemplated for practicing the described implementations. This
description is not to be taken in a limiting sense, but rather is made
merely for the purpose of describing the general principles of the
implementations. The scope of the described implementations should be
ascertained with reference to the issued claims. In the description that
follows, like numerals or reference designators will be used to reference
like parts or elements throughout.

Overview

[0026] As described herein, various exemplary electrodes and associated
techniques can enhance localization for lead or electrode placement and
navigation or physiologic mapping. For example, an exemplary electrode
array and switching mechanism allows for sequential acquisition of
potentials in a field generated by applied current. In such an example,
the acquired potentials can be used to locate the array in a local
coordinate system (e.g., including yaw, pitch and roll) or to compensate
for field heterogeneities and thereby enhance location accuracy. In
another example, an exemplary electrode array provides multiple, discrete
electrical centers (e.g., geometric centers for electrodes of same
characteristics), which may be selectable via a switching mechanism.
Various other examples are described below.

Exemplary Stimulation Device

[0027] The techniques described below may be implemented in connection
with a device configured or configurable to deliver cardiac therapy or to
monitor cardiac condition.

[0028] FIG. 1 shows an exemplary stimulation device 100 in electrical
communication with a patient's heart 102 by way of three leads (a right
atrial lead 104, a left ventricular lead 106 and a right ventricular lead
108), suitable for delivering multi-chamber stimulation and shock
therapy. The leads 104, 106, 108 are optionally configurable for delivery
of stimulation pulses suitable for stimulation of nerves or other tissue.
In addition, in the example of FIG. 1, the device 100 includes a fourth
lead 110 having multiple electrodes 144, 144', 144'' suitable for
stimulation of tissue and/or sensing of physiologic signals. This lead
may be positioned in and/or near a patient's heart and/or remote from the
heart.

[0029] FIG. 1 also shows approximate locations of the right and left
phrenic nerves 154, 158. The phrenic nerve is made up mostly of motor
nerve fibres for producing contractions of the diaphragm. In addition, it
provides sensory innervation for various components of the mediastinum
and pleura, as well as the upper abdomen (e.g., liver and gall bladder).
The right phrenic nerve 154 passes over the brachiocephalic artery,
posterior to the subclavian vein, and then crosses the root of the right
lung anteriorly and then leaves the thorax by passing through the vena
cava hiatus opening in the diaphragm at the level of T8. More
specifically, with respect to the heart, the right phrenic nerve 154
passes over the right atrium while the left phrenic nerve 158 passes over
the pericardium of the left ventricle and pierces the diaphragm
separately. While certain therapies may call for phrenic nerve
stimulation (e.g., for treatment of sleep apnea), in general, cardiac
pacing therapies avoid phrenic nerve stimulation through judicious lead
and electrode placement, selection of electrode configurations,
adjustment of pacing parameters, etc.

[0030] Referring again to the various leads of the device 100, the right
atrial lead 104, as the name implies, is positioned in and/or passes
through a patient's right atrium. The right atrial lead 104 is configured
to sense atrial cardiac signals and/or to provide right atrial chamber
stimulation therapy. As described further below, the right atrial lead
104 may be used by the device 100 to acquire far-field ventricular signal
data. As shown in FIG. 1, the right atrial lead 104 includes an atrial
tip electrode 120, which typically is implanted in the patient's right
atrial appendage, and an atrial ring electrode 121. The right atrial lead
104 may have electrodes other than the tip 120 and ring 121 electrodes.
Further, the right atrial lead 104 may include electrodes suitable for
stimulation and/or sensing located on a branch.

[0031] To sense atrial cardiac signals, ventricular cardiac signals and/or
to provide chamber pacing therapy, particularly on the left side of a
patient's heart, the stimulation device 100 is coupled to the left
ventricular lead 106, which in FIG. 1 is also referred to as a coronary
sinus lead as it is designed for placement in the coronary sinus and/or
tributary veins of the coronary sinus. As shown in FIG. 1, the coronary
sinus lead 106 is configured to position at least one distal electrode
adjacent to the left ventricle and/or additional electrode(s) adjacent to
the left atrium. In a normal heart, tributary veins of the coronary sinus
include, but may not be limited to, the great cardiac vein, the left
marginal vein, the left posterior ventricular vein, the middle cardiac
vein, and the small cardiac vein.

[0032] In the example of FIG. 1, the coronary sinus lead 106 includes a
series of electrodes 123. In particular, a series of four electrodes are
shown positioned in an anterior vein of the heart 102. Other coronary
sinus leads may include a different number of electrodes than the lead
106. As described herein, an exemplary method selects one or more
electrodes (e.g., from electrodes 123 of the lead 106) and determines
characteristics associated with conduction and/or timing in the heart to
aid in ventricular pacing therapy and/or assessment of cardiac condition.
As described in more detail below, an illustrative method acquires
information using various electrode configurations where an electrode
configuration typically includes at least one electrode of a coronary
sinus lead or other type of left ventricular lead. Such information may
be used to determine a suitable electrode configuration for the lead 106
(e.g., selection of one or more electrodes 123 of the lead 106).

[0033] In the example of FIG. 1, as connected to the device 100, the
coronary sinus lead 106 is configured for acquisition of ventricular
cardiac signals (and optionally atrial signals) and to deliver left
ventricular pacing therapy using, for example, at least one of the
electrodes 123 and/or the tip electrode 122. The lead 106 optionally
allows for left atrial pacing therapy, for example, using at least the
left atrial ring electrode 124. The lead 106 optionally allows for
shocking therapy, for example, using at least the left atrial coil
electrode 126. For a complete description of a particular coronary sinus
lead, the reader is directed to U.S. Pat. No. 5,466,254, "Coronary Sinus
Lead with Atrial Sensing Capability" (Helland), which is incorporated
herein by reference.

[0034] The stimulation device 100 is also shown in electrical
communication with the patient's heart 102 by way of an implantable right
ventricular lead 108 having, in this exemplary implementation, a right
ventricular tip electrode 128, a right ventricular ring electrode 130, a
right ventricular (RV) coil electrode 132, and an SVC coil electrode 134.
Typically, the right ventricular lead 108 is transvenously inserted into
the heart 102 to place the right ventricular tip electrode 128 in the
right ventricular apex so that the RV coil electrode 132 will be
positioned in the right ventricle and the SVC coil electrode 134 will be
positioned in the superior vena cava. Accordingly, the right ventricular
lead 108, as connected to the device 100, is capable of sensing or
receiving cardiac signals, and delivering stimulation in the form of
pacing and shock therapy to the right ventricle. An exemplary right
ventricular lead may also include at least one electrode capable of
stimulating other tissue; such an electrode may be positioned on the lead
or a bifurcation or leg of the lead. A right ventricular lead may include
a series of electrodes, such as the series 123 of the left ventricular
lead 106.

[0035] FIG. 1 also shows a lead 160 as including several electrode arrays
163. In the example of FIG. 1, each electrode array 163 of the lead 160
includes a series of electrodes 162 with an associated circuit 168.
Conductors 164 provide an electrical supply and return for the circuit
168. The circuit 168 includes control logic sufficient to electrically
connect the conductors 164 to one or more of the electrodes of the series
162. In the example of FIG. 1, the lead 160 includes a lumen 166 suitable
for receipt of a guidewire to facilitate placement of the lead 160. As
described herein, any of the leads 104, 106, 108 or 110 may include one
or more electrode array, optionally configured as the electrode array 163
of the lead 160. For example, the lead 106 may include features of the
lead 160 and be suitable for multisite pacing for cardiac
resynchronization therapy (CRT).

[0036] FIG. 2 shows an exemplary, simplified block diagram depicting
various components of the device 100. The device 100 can be capable of
treating both fast and slow arrhythmias with stimulation therapy,
including cardioversion, defibrillation, and pacing stimulation. While a
particular multi-chamber device is shown, it is to be appreciated and
understood that this is for illustration purposes only. Thus, the
techniques, methods, etc., described below can be implemented in
connection with any suitably configured or configurable device.
Accordingly, one of skill in the art could readily duplicate, eliminate,
or disable the appropriate circuitry in any desired combination to
provide a device capable of treating the appropriate chamber(s) or
regions of a patient's heart.

[0037] Housing 200 for the device 100 is often referred to as the "can",
"case" or "case electrode", and may be programmably selected to act as
the return electrode for all "unipolar" modes. As described below,
various exemplary techniques implement unipolar sensing for data that may
include indicia of functional conduction block in myocardial tissue.
Housing 200 may further be used as a return electrode alone or in
combination with one or more of the coil electrodes 126, 132 and 134 for
shocking or other purposes. Housing 200 further includes a connector (not
shown) having a plurality of terminals 201, 202, 204, 206, 208, 212, 214,
216, 218, 221, 223 (shown schematically and, for convenience, the names
of the electrodes to which they are connected are shown next to the
terminals).

[0038] To achieve right atrial sensing, pacing and/or other tissue
sensing, stimulation, etc., the connector includes at least a right
atrial tip terminal (AR TIP) 202 adapted for connection to the right
atrial tip electrode 120. A right atrial ring terminal (AR RING) 201
is also shown, which is adapted for connection to the right atrial ring
electrode 121. To achieve left chamber sensing, pacing, shocking, and/or
other tissue sensing, stimulation, etc., the connector includes at least
a left ventricular tip terminal (VL TIP) 204, a left atrial ring
terminal (AL RING) 206, and a left atrial shocking terminal (AL
COIL) 208, which are adapted for connection to the left ventricular tip
electrode 122, the left atrial ring electrode 124, and the left atrial
coil electrode 126, respectively. Connection to suitable stimulation
electrodes is also possible via these and/or other terminals (e.g., via a
stimulation terminal S ELEC 221). The terminal S ELEC 221 may optionally
be used for sensing. For example, electrodes of the lead 110 may connect
to the device 100 at the terminal 221 or optionally at one or more other
terminals.

[0039] A terminal 223 allows for connection of a series of left
ventricular electrodes. For example, the series of four electrodes 123 of
the lead 106 may connect to the device 100 via the terminal 223. The
terminal 223 and an electrode configuration switch 226 allow for
selection of one or more of the series of electrodes and hence electrode
configuration. In the example of FIG. 2, the terminal 223 includes four
branches to the switch 226 where each branch corresponds to one of the
four electrodes 123.

[0040] As described herein, a terminal or terminals may allow for
transmission of information to a lead that includes a control circuit
such as the lead 160 of FIG. 1. For example, a terminal may transmit a
signal that causes the circuit 168 to select one or more of the
electrodes 162 for delivery of energy to the body, for sensing electrical
activity of the body or for delivery of energy and sensing activity.

[0041] To support right chamber sensing, pacing, shocking, and/or other
tissue sensing, stimulation, etc., the connector further includes a right
ventricular tip terminal (VR TIP) 212, a right ventricular ring
terminal (VR RING) 214, a right ventricular shocking terminal (RV
COIL) 216, and a superior vena cava shocking terminal (SVC COIL) 218,
which are adapted for connection to the right ventricular tip electrode
128, right ventricular ring electrode 130, the RV coil electrode 132, and
the SVC coil electrode 134, respectively.

[0042] At the core of the stimulation device 100 is a programmable
microcontroller 220 that controls the various modes of cardiac or other
therapy. As is well known in the art, microcontroller 220 typically
includes a microprocessor, or equivalent control circuitry, designed
specifically for controlling the delivery of stimulation therapy, and may
further include RAM or ROM memory, logic and timing circuitry, state
machine circuitry, and I/O circuitry. Typically, microcontroller 220
includes the ability to process or monitor input signals (data or
information) as controlled by a program code stored in a designated block
of memory. The type of microcontroller is not critical to the described
implementations. Rather, any suitable microcontroller 220 may be used
that is suitable to carry out the functions described herein. The use of
microprocessor-based control circuits for performing timing and data
analysis functions are well known in the art.

[0043] Representative types of control circuitry that may be used in
connection with the described embodiments can include the
microprocessor-based control system of U.S. Pat. No. 4,940,052, the
state-machine of U.S. Pat. Nos. 4,712,555 and 4,944,298, all of which are
incorporated by reference herein. For a more detailed description of the
various timing intervals used within the stimulation device and their
inter-relationship, see U.S. Pat. No. 4,788,980, also incorporated herein
by reference.

[0044] FIG. 2 also shows an atrial pulse generator 222 and a ventricular
pulse generator 224 that generate pacing stimulation pulses for delivery
by the right atrial lead 104, the coronary sinus lead 106, and/or the
right ventricular lead 108 via an electrode configuration switch 226. It
is understood that in order to provide stimulation therapy in each of the
four chambers of the heart (or to other tissue) the atrial and
ventricular pulse generators, 222 and 224, may include dedicated,
independent pulse generators, multiplexed pulse generators, or shared
pulse generators. The pulse generators 222 and 224 are controlled by the
microcontroller 220 via appropriate control signals 228 and 230,
respectively, to trigger or inhibit the stimulation pulses.

[0045] The microcontroller 220 further includes timing control circuitry
232 to control the timing of the stimulation pulses (e.g., pacing rate,
atrio-ventricular (AV) delay, interatrial conduction (AA) delay, or
interventricular conduction (VV) delay, etc.) as well as to keep track of
the timing of refractory periods, blanking intervals, noise detection
windows, evoked response windows, alert intervals, marker channel timing,
etc., which is well known in the art.

[0046] The microcontroller 220 further includes an arrhythmia detector
234. The detector 234 can be utilized by the stimulation device 100 for
determining desirable times to administer various therapies. The detector
234 may be implemented in hardware as part of the microcontroller 220, or
as software/firmware instructions programmed into the device and executed
on the microcontroller 220 during certain modes of operation.

[0047] Microcontroller 220 further includes a morphology discrimination
module 236, a capture detection module 237 and an auto sensing module
238. These modules are optionally used to implement various exemplary
recognition algorithms and/or methods presented below. The aforementioned
components may be implemented in hardware as part of the microcontroller
220, or as software/firmware instructions programmed into the device and
executed on the microcontroller 220 during certain modes of operation.
The capture detection module 237, as described herein, may aid in
acquisition, analysis, etc., of information relating to IEGMs and, in
particular, act to distinguish capture versus non-capture versus fusion.

[0048] The electronic configuration switch 226 includes a plurality of
switches for connecting the desired electrodes to the appropriate I/O
circuits, thereby providing complete electrode programmability.
Accordingly, switch 226, in response to a control signal 242 from the
microcontroller 220, determines the polarity of the stimulation pulses
(e.g., unipolar, bipolar, etc.) by selectively closing the appropriate
combination of switches (not shown) as is known in the art.

[0049] Atrial sensing circuits 244 and ventricular sensing circuits 246
may also be selectively coupled to the right atrial lead 104, coronary
sinus lead 106, and the right ventricular lead 108, through the switch
226 for detecting the presence of cardiac activity in each of the four
chambers of the heart. Accordingly, the atrial and ventricular sensing
circuits, 244 and 246, may include dedicated sense amplifiers,
multiplexed amplifiers, or shared amplifiers. Switch 226 determines the
"sensing polarity" of the cardiac signal by selectively closing the
appropriate switches, as is also known in the art. In this way, the
clinician may program the sensing polarity independent of the stimulation
polarity. The sensing circuits (e.g., 244 and 246) are optionally capable
of obtaining information indicative of tissue capture.

[0050] Each of the sensing circuits 244 and 246 preferably employs one or
more low power, precision amplifiers with programmable gain and/or
automatic gain control, bandpass filtering, and a threshold detection
circuit, as known in the art, to selectively sense the cardiac signal of
interest. The automatic gain control enables the device 100 to deal
effectively with the difficult problem of sensing the low amplitude
signal characteristics of atrial or ventricular fibrillation.

[0051] The outputs of the atrial and ventricular sensing circuits 244 and
246 are connected to the microcontroller 220, which, in turn, is able to
trigger or inhibit the atrial and ventricular pulse generators 222 and
224, respectively, in a demand fashion in response to the absence or
presence of cardiac activity in the appropriate chambers of the heart.
Furthermore, as described herein, the microcontroller 220 is also capable
of analyzing information output from the sensing circuits 244 and 246
and/or the data acquisition system 252 to determine or detect whether and
to what degree tissue capture has occurred and to program a pulse, or
pulses, in response to such determinations. The sensing circuits 244 and
246, in turn, receive control signals over signal lines 248 and 250 from
the microcontroller 220 for purposes of controlling the gain, threshold,
polarization charge removal circuitry (not shown), and the timing of any
blocking circuitry (not shown) coupled to the inputs of the sensing
circuits, 244 and 246, as is known in the art.

[0052] For arrhythmia detection, the device 100 may utilize the atrial and
ventricular sensing circuits, 244 and 246, to sense cardiac signals to
determine whether a rhythm is physiologic or pathologic. Of course, other
sensing circuits may be available depending on need and/or desire. In
reference to arrhythmias, as used herein, "sensing" is reserved for the
noting of an electrical signal or obtaining data (information), and
"detection" is the processing (analysis) of these sensed signals and
noting the presence of an arrhythmia or of a precursor or other factor
that may indicate a risk of or likelihood of an imminent onset of an
arrhythmia.

[0053] The exemplary detector module 234, optionally uses timing intervals
between sensed events (e.g., P-waves, R-waves, and depolarization signals
associated with fibrillation) and to perform one or more comparisons to a
predefined rate zone limit (i.e., bradycardia, normal, low rate VT, high
rate VT, and fibrillation rate zones) and/or various other
characteristics (e.g., sudden onset, stability, physiologic sensors, and
morphology, etc.) in order to determine the type of remedial therapy
(e.g., anti-arrhythmia, etc.) that is desired or needed (e.g.,
bradycardia pacing, anti-tachycardia pacing, cardioversion shocks or
defibrillation shocks, collectively referred to as "tiered therapy").
Similar rules can be applied to the atrial channel to determine if there
is an atrial tachyarrhythmia or atrial fibrillation with appropriate
classification and intervention.

[0054] Cardiac signals are also applied to inputs of an analog-to-digital
(A/D) data acquisition system 252. The data acquisition system 252 is
configured to acquire intracardiac electrogram (IEGM) signals or other
action potential signals, convert the raw analog data into a digital
signal, and store the digital signals for later processing and/or
telemetric transmission to an external device 254. The data acquisition
system 252 is coupled to the right atrial lead 104, the coronary sinus
lead 106, the right ventricular lead 108 and/or another lead (e.g., the
lead 110) through the switch 226 to sample cardiac signals or other
signals across any pair or other number of desired electrodes. A control
signal 256 from the microcontroller 220 may instruct the A/D 252 to
operate in a particular mode (e.g., resolution, amplification, etc.).

[0055] Various exemplary mechanisms for signal acquisition are described
herein that optionally include use of one or more analog-to-digital
converter. Various exemplary mechanisms allow for adjustment of one or
more parameter associated with signal acquisition.

[0056] The microcontroller 220 is further coupled to a memory 260 by a
suitable data/address bus 262, wherein the programmable operating
parameters used by the microcontroller 220 are stored and modified, as
required, in order to customize the operation of the stimulation device
100 to suit the needs of a particular patient. Such operating parameters
define, for example, pacing pulse amplitude, pulse duration, electrode
polarity, rate, sensitivity, automatic features, arrhythmia detection
criteria, and the amplitude, waveshape, number of pulses, and vector of
each shocking pulse to be delivered to the patient's heart 102 within
each respective tier of therapy. One feature of the described embodiments
is the ability to sense and store a relatively large amount of data
(e.g., from the data acquisition system 252), which data may then be used
for subsequent analysis to guide the programming and operation of the
device 100.

[0057] Advantageously, the operating parameters of the implantable device
100 may be non-invasively programmed into the memory 260 through a
telemetry circuit 264 in telemetric communication via communication link
266 with the external device 254, such as a programmer, transtelephonic
transceiver, or a diagnostic system analyzer. The microcontroller 220
activates the telemetry circuit 264 with a control signal 268. The
telemetry circuit 264 advantageously allows intracardiac electrograms
(IEGM) and other information (e.g., status information relating to the
operation of the device 100, etc., as contained in the microcontroller
220 or memory 260) to be sent to the external device 254 through an
established communication link 266.

[0058] The stimulation device 100 can further include one or more
physiologic sensors 270. For example, the device 100 may include a
"rate-responsive" sensor that may provide, for example, information to
aid in adjustment of pacing stimulation rate according to the exercise
state of the patient. However, the one or more physiological sensors 270
may further be used to detect changes in cardiac output (see, e.g., U.S.
Pat. No. 6,314,323, entitled "Heart stimulator determining cardiac
output, by measuring the systolic pressure, for controlling the
stimulation", to Ekwall, issued Nov. 6, 2001, which discusses a pressure
sensor adapted to sense pressure in a right ventricle and to generate an
electrical pressure signal corresponding to the sensed pressure, an
integrator supplied with the pressure signal which integrates the
pressure signal between a start time and a stop time to produce an
integration result that corresponds to cardiac output), changes in the
physiological condition of the heart, or diurnal changes in activity
(e.g., detecting sleep and wake states). Accordingly, the microcontroller
220 responds by adjusting the various pacing parameters (such as rate, AV
Delay, VV Delay, etc.) at which the atrial and ventricular pulse
generators, 222 and 224, generate stimulation pulses.

[0059] While shown as being included within the stimulation device 100, it
is to be understood that one or more of the physiologic sensors 270 may
also be external to the stimulation device 100, yet still be implanted
within or carried by the patient. Examples of physiologic sensors that
may be implemented in device 100 include known sensors that, for example,
sense respiration rate, oxygen concentration of blood, pH of blood,
CO2 concentration of blood, ventricular gradient, cardiac output,
preload, afterload, contractility, and so forth. Another sensor that may
be used is one that detects activity variance, wherein an activity sensor
is monitored diurnally to detect the low variance in the measurement
corresponding to the sleep state. For a complete description of the
activity variance sensor, the reader is directed to U.S. Pat. No.
5,476,483 which is hereby incorporated by reference.

[0060] The one or more physiologic sensors 270 optionally include sensors
for detecting movement and minute ventilation in the patient. Signals
generated by a position sensor, a MV sensor, etc., may be passed to the
microcontroller 220 for analysis in determining whether to adjust the
pacing rate, etc. The microcontroller 220 may monitor the signals for
indications of the patient's position and activity status, such as
whether the patient is climbing upstairs or descending downstairs or
whether the patient is sitting up after lying down.

[0061] The stimulation device 100 additionally includes a battery 276 that
provides operating power to all of the circuits shown in FIG. 2. For the
stimulation device 100, which employs shocking therapy, the battery 276
is capable of operating at low current drains for long periods of time
(e.g., preferably less than 10 μA), and is capable of providing
high-current pulses (for capacitor charging) when the patient requires a
shock pulse (e.g., preferably, in excess of 2 A, at voltages above 200 V,
for periods of 10 seconds or more). The battery 276 also desirably has a
predictable discharge characteristic so that elective replacement time
can be detected.

[0062] The stimulation device 100 can further include magnet detection
circuitry (not shown), coupled to the microcontroller 220, to detect when
a magnet is placed over the stimulation device 100. A magnet may be used
by a clinician to perform various test functions of the stimulation
device 100 and/or to signal the microcontroller 220 that the external
programmer 254 is in place to receive or transmit data to the
microcontroller 220 through the telemetry circuits 264.

[0063] The stimulation device 100 further includes an impedance measuring
circuit 278 that is enabled by the microcontroller 220 via a control
signal 280. The known uses for an impedance measuring circuit 278
include, but are not limited to, lead impedance surveillance during the
acute and chronic phases for proper lead positioning or dislodgement;
detecting operable electrodes and automatically switching to an operable
pair if dislodgement occurs; measuring respiration or minute ventilation;
measuring thoracic impedance for determining shock thresholds; detecting
when the device has been implanted; measuring stroke volume; and
detecting the opening of heart valves, etc. The impedance measuring
circuit 278 is advantageously coupled to the switch 226 so that any
desired electrode may be used.

[0064] In the case where the stimulation device 100 is intended to operate
as an implantable cardioverter/defibrillator (ICD) device, it detects the
occurrence of an arrhythmia, and automatically applies an appropriate
therapy to the heart aimed at terminating the detected arrhythmia. To
this end, the microcontroller 220 further controls a shocking circuit 282
by way of a control signal 284. The shocking circuit 282 generates
shocking pulses of low (e.g., up to 0.5 J), moderate (e.g., 0.5 J to 10
J), or high energy (e.g., 11 J to 40 J), as controlled by the
microcontroller 220. Such shocking pulses are applied to the patient's
heart 102 through at least two shocking electrodes, and as shown in this
embodiment, selected from the left atrial coil electrode 126, the RV coil
electrode 132, and/or the SVC coil electrode 134. As noted above, the
housing 200 may act as an active electrode in combination with the RV
electrode 132, or as part of a split electrical vector using the SVC coil
electrode 134 or the left atrial coil electrode 126 (i.e., using the RV
electrode as a common electrode).

[0065] Cardioversion level shocks are generally considered to be of low to
moderate energy level (so as to minimize pain felt by the patient),
and/or synchronized with an R-wave and/or pertaining to the treatment of
tachycardia. Defibrillation shocks are generally of moderate to high
energy level (e.g., corresponding to thresholds in the range of
approximately 5 J to 40 J), delivered asynchronously (since R-waves may
be too disorganized), and pertaining exclusively to the treatment of
fibrillation. Accordingly, the microcontroller 220 is capable of
controlling the synchronous or asynchronous delivery of the shocking
pulses.

[0066] As already mentioned, the implantable device 100 includes impedance
measurement circuitry 278. Such a circuit may measure impedance or
electrical resistance through use of various techniques. For example, the
device 100 may deliver a low voltage (e.g., about 10 mV to about 20 mV)
of alternating current between the RV tip electrode 128 and the case
electrode 200. During delivery of this energy, the device 100 may measure
resistance between these two electrodes where the resistance depends on
any of a variety of factors. For example, the resistance may vary
inversely with respect to volume of blood along the path.

[0067] In another example, resistance measurement occurs through use of a
four terminal or electrode technique. For example, the exemplary device
100 may deliver an alternating current between one of the RV tip
electrode 128 and the case electrode 200. During delivery, the device 100
may measure a potential between the RA ring electrode 121 and the RV ring
electrode 130 where the potential is proportional to the resistance
between the selected potential measurement electrodes.

[0068] With respect to two terminal or electrode techniques, where two
electrodes are used to introduce current and the same two electrodes are
used to measure potential, parasitic electrode-electrolyte impedances can
introduce noise, especially at low current frequencies; thus, a greater
number of terminals or electrodes may be used. For example,
aforementioned four electrode techniques, where one electrode pair
introduces current and another electrode pair measures potential, can
cancel noise due to electrode-electrolyte interface impedance.
Alternatively, where suitable or desirable, a two terminal or electrode
technique may use larger electrode areas (e.g., even exceeding about 1
cm2) and/or higher current frequencies (e.g., above about 10 kHz) to
reduce noise.

[0069] Various exemplary electrodes and associated techniques can enhance
localization for lead or electrode placement and navigation or
physiologic mapping. With respect to the ENSITE® NAVX®
localization system, heterogeneities in a current generated field can
introduce errors in locating an electrode. In general, such a
localization system locates the "electrical center" of an electrode,
which is, in most situations, equivalent to the electrode's geometric
center. Thus, as electrode size increases, an electrode will occupy a
larger portion of a field and likely be exposed to more field
heterogeneity. Consequently, a large electrode will be at greater risk of
being inaccurately located by such a localization system. For a small
electrode, a risk exists that it will be located entirely in a
heterogeneous portion of a field, which can give rise to an inaccurate
position determination.

[0070] Various exemplary electrodes and associated switching mechanisms or
more generally acquisition mechanisms can measure or uncover field
heterogeneities and thereby enhance location accuracy of a localization
system. Further, various exemplary electrodes may be shaped to have
geometric centers that are "asymmetric" along one or more axes (or axes
of rotation). Yet further, various exemplary electrodes may be arranged
as arrays where acquisition or processing of acquired information
provides an indication of electrode or lead direction. Additionally,
where dimensions of an electrode or an electrode array are known, the
dimensions may be used to map field heterogeneities and ultimately
compensate for such heterogeneities to improve accuracy of position
determinations.

[0071] The ENSITE® NAVX® localization system includes a feature
called "Field Scaling" that measures local variations point-by-point
based on a known distance between electrodes on a lead and applies
correction factors for these local variations, for example, to more
accurately display anatomic features and electrode positions. Various
exemplary technologies described herein can operate in conjunction with
this feature to enhance performance of the localization system for
position and motion of electrodes, for display of anatomy or for
computation of motion-based hemodynamic surrogates.

[0072] FIG. 3 shows an exemplary method 300 for acquiring and analyzing
position information using a catheter or a lead with a specialized
electrode or electrodes. In the description that follows, the term "lead"
is used, at times, to include "catheter". In the example of FIG. 3, the
method 300 includes a configurations block 310 that includes
intraoperative configurations 312 (e.g., acute configurations) and
chronic configurations 314. The intraoperative configurations 312 pertain
to configurations that may be achieved during an operative procedure. For
example, during an operative procedure, one or more leads may be
positioned in a patient where the one or more leads are connected to, or
variously connectable to, a device configured to acquire information and
optionally to deliver electrical energy to the patient (e.g., to the
heart, to a nerve, to other tissue, etc.). The chronic configurations 314
pertain to configurations achievable by a chronically implanted device
and its associated lead or leads, or more generally, its electrode
arrangements. In general, intraoperative configurations include those
achievable by physically re-positioning a lead in a patient's body while
chronic configurations normally do not allow for re-positioning as a lead
or leads are usually anchored during implantation or become anchored in
the weeks to months after implantation. Chronic configurations do,
however, include selection of a subset of the multiple implanted
electrodes, for example using a distal tip electrode versus a less distal
electrode as a cathode or using the distal electrode and the less distal
electrode as a bipolar pair versus using these electrodes as two
independent cathodes (e.g., as independent unipolar configurations).
Thus, intraoperative configurations include configurations available by
changing device settings, electrode selection, and physical position of
electrodes, while chronic configurations include only those
configurations available by changing device settings and electrode
selection, or "electronic repositioning" of one or more stimulation
electrodes.

[0073] As indicated in FIG. 3, an acquisition block 320 includes
acquisition of position information 322 and optionally acquisition of
other information 324 (e.g., electrical information as to field
homogeneity or heterogeneity, electrical activity of the heart, biosensor
information, etc.). While an arrow indicates that a relationship or
relationships may exist between the configurations block 310 and the
acquisition block 320, acquisition of information may occur by using in
part an electrode (or other equipment) that is not part of a
configuration. For example, the acquisition block 320 may rely on one or
more surface electrodes that define a coordinate system or location
system for locating an electrode that defines one or more configurations.
For example, three pairs of surface electrodes positioned on a patient
may be configured to deliver current and define a three-dimensional space
whereby measurement of a potential locates an electrode or electrodes in
the three-dimensional space.

[0074] As described herein, an electrode may be configured for delivery of
energy to the heart; for acquisition of electrical information; for
acquisition of position information; for acquisition of electrical
information and position information; for delivery of energy to the heart
and for acquisition of electrical information; for delivery of energy to
the heart and for acquisition of position information; for delivery of
energy to the heart, for acquisition of electrical information and for
acquisition of position information.

[0075] In various examples, acquisition of position information occurs by
measuring one or more potentials where the measuring relies on an
electrode or electrodes that may also be configured to deliver energy to
the heart (e.g., electrical energy to pace a chamber of the heart). In
such a scenario, the electrode may deliver energy sufficient to stimulate
the heart and then be tracked along one or more dimensions to monitor the
positional consequences of the stimulation. Further, such an electrode or
electrodes may be used to acquire electrical information (e.g., an IEGM
that evidences an evoked response). Such an electrode or electrodes can
perform all three of these tasks with proper circuitry and control. For
example, after delivery of the energy, an electrode may be configured for
acquiring one or more potentials related to location and for acquiring an
electrogram. To acquire potentials and an electrogram, circuitry may
include gating or other sampling techniques (e.g., to avoid circuitry or
interference issues). Such circuitry may rely on one sampling frequency
for acquiring potentials for motion tracking and another sampling
frequency for acquiring an electrogram.

[0076] The method 300 of FIG. 3 includes a determination block 330 for
determining one or more of cardiac position 332, respiratory position 334
(e.g., position in the body as affected by respiration), electrode
position 336 and lead position 338.

[0077] As shown in the example of FIG. 3, the conclusion block 340 may
perform actions such as to optimize therapy 342 and/or to monitor patient
and/or device condition 344. Information 320 or determinations 330 may be
mapped or otherwise displayed with respect to anatomical features or
markers. For example, as described herein, the determinations as to
electrode position 336 can be used to map field heterogeneities in a
multidimensional field and to compensate for such heterogeneities to
improve accuracy of future position determinations. While electrical
impedance tomography relies on heterogeneities to image internal
physiology, various techniques described herein measure heterogeneities
in a field and compensate for such heterogeneities to increase accuracy
of position determinations.

[0078] As described herein, an exemplary method can include: positioning
one or more electrodes within the heart and/or surrounding space (e.g.,
intra-chamber, intra-vascular, intrapericardial, etc., which may be
collectively referred to as "cardiac space"); and acquiring information
(e.g., via one or more measured potentials) to determine a location,
locations or displacement for at least one of the one or more electrodes
using a localization system (e.g., the ENSITE® NAVX® system or
other system with appropriate features). In such a method, the positioned
electrodes may be configured for acquisition of electrical information
(e.g., IEGMs). Further, with respect to acquisition of information, an
acquisition system may operate at an appropriate sampling rate. For
example, an acquisition system for position information may operate at a
sampling rate of about 100 Hz (e.g., the ENSITE® NAVX® system can
sample at about 93 Hz) and an acquisition system for electrical
information may operate at a sampling rate of about 1200 Hz (e.g., in
unipolar, bipolar or other polar arrangement).

[0079] Further, for an electrode array or series of electrodes, an offset
or interleaving technique may be applied to acquire information from
individual electrodes or groups of electrodes. A localization system or
lead system may include a parallel interface, a serial interface or a
parallel interface and a serial interface. Multiplexers or the like may
be configured as a switch for an acquisition channel or channels. As
explained with respect to the lead 160 of FIG. 1, one or more small scale
circuits may be integrated into a lead (e.g., along a lead body, a lead
connector or at or near an electrode array). For example, an
application-specific integrated circuit (ASIC) may be provided for
selectable acquisition of information from one or more electrodes or for
delivery of energy by one or more electrodes. Small-scale multiplexers
(MUX), including amplifiers, buffers, timers and the like, are
commercially available and may be suitable for use with exemplary
electrodes described herein.

[0080] An exemplary method may include preparing a patient for both
implant of a device such as the device 100 of FIGS. 1 and 2 and for study
using a localization system. Such preparation may occur in a relatively
standard manner for implant prep, and using the ENSITE® NAVX®
system or other similar technology. As described herein, any of a variety
of electroanatomic mapping or localization systems that can locate
indwelling electrodes in and around the heart may be used.

[0081] Once prepped, a clinician or robot may place leads and/or catheters
in the patient's body, including any leads to be chronically implanted as
part of a CRT system, as well as optional additional electrodes that may
yield additional information (e.g., to increase accuracy by providing
global information or other information).

[0082] After an initial placement of an electrode-bearing catheter or an
electrode-bearing lead, a clinician may then connect one or more
electrodes to an electroanatomic mapping or localization system. The term
"connection" can refer to physical electrical connection or wireless
connection (e.g., telemetric, RF, ultrasound, etc.) with the electrodes
or wireless connection with another device that is in electrical contact
with the electrodes.

[0083] Once an appropriate connection or connections have been made,
real-time position data for one or more electrodes may be acquired for
various configurations or conditions. For example, position data may be
acquired during normal sinus rhythm; pacing in one or more chambers;
advancing, withdrawing, or moving a location of an electrode; pacing one
or more different electrode configurations (e.g. multisite pacing); or
varying inter-stimulus timing (e.g. AV delay, VV delay).

[0084] In various examples, simultaneous to the acquisition of position
information, an intracardiac electrogram (IEGM) from each electrode can
also be acquired and associated with the anatomic position of the
electrode. While various examples refer to simultaneous acquisition,
acquisition of electrical information and acquisition of mechanical
information may occur sequentially (e.g., alternate cardiac cycles) or
interleaved (e.g., both acquired during the same cardiac cycle but offset
by sampling time or sampling frequency).

[0085] In various exemplary methods, electrodes within the cardiac space
may be optionally positioned at various locations (e.g., by continuous
movement or by discrete, sequential moves), with a mapping system
recording the real-time motion information at each electrode position in
a point-by-point manner. Such motion data can by associated with a
respective anatomic point from which it was collected. By moving the
electrodes from point to point during an intervention, the motion data
from each location can be incorporated into a single map, model, or
parameter.

[0086] An exemplary method may include determining one or more parameters
where an algorithm or a clinician may select a configuration (e.g.,
electrode location, multisite arrangement, AV/VV timing) that yielded the
best value for one or more parameters of a CRT system and use the
selected configuration as a chronic configuration for the CRT system.
Such a chronic configuration may be optionally updated from time to time
(e.g., during a follow-up visit, in a patient environment, etc.,
depending on specific capabilities of a system).

[0087] Various exemplary methods, using either a single parameter or a
combination of more than one parameter, may automatically select a
configuration, present an optimal configuration for acknowledgement by a
clinician, or present various configurations to a clinician along with
pros and cons of each configuration (e.g., in objective or subjective
terms). For example, a particular configuration may be associated with a
high power usage that may excessively drain a power source of an
implantable device (e.g., device battery 276). Other pros and cons may
pertain to patient comfort (e.g., pain, lack of pain, overall feeling,
etc.).

[0088] An exemplary method may rely on certain equipment at time of
implant or exploration and other equipment after implantation of a device
to deliver a cardiac therapy. For example, during an intraoperative
procedure, wireless communication may not be required; whereas, during a
follow-up visit, measured potentials for position of chronically
implanted electrodes and of measured IEGMs using chronically implanted
electrodes may be communicated wirelessly from an implanted device to an
external device. With respect to optimization of a chronically implanted
system, in general, electrode location will not be altered, but other
parameters altered to result in an optimal configuration (e.g., single-
or multi-site arrangement, polarity, stimulation energy, timing
parameters, etc.).

[0089] As discussed herein, various exemplary techniques deliver current
and measure potential where potential varies typically with respect to
cardiac mechanics (e.g., due to motion). For example, electrodes for
delivery of current may be placed at locations that do not vary
significantly with respect to cardiac mechanics while one or more
electrodes for measuring potential may be placed at a location or
locations that vary with respect to cardiac mechanics. Alternatively,
electrodes for measuring potential may be placed at locations that do not
vary significantly with respect to cardiac mechanics while one or more
electrodes for delivery of current may be placed at a location or
locations that vary with respect to cardiac mechanics. Various
combinations of the foregoing arrangements are possible as well.
Electrodes may be associated with a catheter or a lead. In some
instances, an electrode may be a "stand-alone" electrode, such as a case
electrode of an implantable device (see, e.g., the case electrode 200 of
the device 100 of FIGS. 1 and 2).

[0090] In accordance with the method 300 of FIG. 3, an exemplary method
may include preparing a patient for both implant and a localization
study. In this example, preparation can be accomplished in standard
manner for implant preparation and the mapping may rely on a localization
system such as the ENSITE® NAVX® system or other similar
technology for the mapping prep. After preparing the patient, the method
includes placing leads and/or catheters in the patient's body, including
any leads to be chronically implanted as part of a therapeutic system.
After placement, the method includes connecting electrodes on leads
and/or catheters to the localization system (e.g., an electroanatomic
mapping system). With respect to the term "connecting", depending on the
equipment, it may include physical electrical connecting and/or
telemetric/RF/wireless/ultrasound/other communication connecting (e.g.,
directly or indirectly, via another "bridging" device, with the
electrodes.)

[0091] After appropriate connections are made, acquiring or recording
follows to record real-time positions of one or more electrodes for
various configurations or conditions such as, but not limited to: normal
sinus rhythm; pacing in one or more chambers (e.g., RV pacing, LV pacing
BiV pacing); at various lead placement locations, (i.e., advancing,
withdrawing, or moving the location of an electrode); pacing one or more
different electrode configurations (e.g. multisite pacing); or varying
inter-stimulus timing (e.g. AV delay, VV delay). After or during
acquisition, the method can determine positions for one or more
electrodes. Subsequently, based on the positions, optionally in
conjunction with other information (e.g., other ENSITE® real-time
cardiac performance parameters), a clinician or a device may select a
configuration (e.g., electrode location, multisite configuration, AV/VV
delays, etc.) that yielded or yields the best value(s) for a mechanical
dyssynchrony parameter(s). This configuration may then be used
chronically (e.g., as the final configuration of a CRT setup).

[0092] Such a method may separately be implemented at a clinic or hospital
follow-up after the time of implant, provided wireless communication with
the chronic indwelling electrodes. In general, it can be assumed that the
electrode location will not be altered, but optimization of single- or
multi-site configuration as well as timing parameter may still be
performed.

[0093] FIG. 4 shows an arrangement and method 400 that may rely in part on
a commercially available system marketed as ENSITE® NAVX®
localization system (see also LOCALISA® system, Medtronic, Inc.,
Minnesota). The ENSITE® NAVX® system is a computerized storage
and display system for use in electrophysiology studies of the human
heart. The system consists of a console workstation, patient interface
unit, and an electrophysiology mapping catheter and/or surface electrode
kit. By visualizing the global activation pattern seen on color-coded
isopotential maps in the system, in conjunction with the reconstructed
electrograms, an electrophysiologist can identify the source of an
arrhythmia and can navigate to a defined area for therapy. The
ENSITE® system is also useful in treating patients with simpler
arrhythmias by providing non-fluoroscopic navigation and visualization of
conventional electrophysiology (EP) catheters.

[0094] As shown in FIG. 4, electrodes 432, 432', which may be part of a
standard EP catheter 430 (or lead), sense electrical potential associated
with current signals transmitted between three pairs of surface electrode
patches 422, 422' (X-axis), 424, 424' (Y-axis) and 426, 426' (Z-axis). An
addition electrode patch 428 is available for reference, grounding or
other function. The ENSITE® NAVX® system can also collect
electrical data from a catheter and can plot a cardiac electrogram from a
particular location (e.g., cardiac vein 103 of heart 102). Information
acquired may be displayed as a 3-D isopotential map and as virtual
electrograms. Repositioning of the catheter allows for plotting of
cardiac electrograms from other locations. Multiple catheters may be used
as well. A cardiac electrogram or electrocardiogram (ECG) of normal heart
activity (e.g., polarization, depolarization, etc.) typically shows
atrial depolarization as a "P wave", ventricular depolarization as an "R
wave", or QRS complex, and repolarization as a "T wave". The ENSITE®
NAVX® system may use electrical information to track or navigate
movement and construct three-dimensional (3-D) models of a chamber of the
heart.

[0095] A clinician can use the ENSITE® NAVX® system to create a
3-D model of a chamber in the heart for purposes of treating arrhythmia
(e.g., treatment via tissue ablation). To create the 3-D model, the
clinician applies surface patches to the body. The ENSITE® NAVX®
system transmits an electrical signal between the patches and the system
then senses the electrical signal using one or more catheters positioned
in the body. The clinician may sweep a catheter with electrodes across a
chamber of the heart to outline structure. Signals acquired during the
sweep, associated with various positions, can then be used to generate a
3-d model. A display can display a diagram of heart morphology, which, in
turn, may help guide an ablation catheter to a point for tissue ablation.

[0096] With respect to the foregoing discussion of current delivery and
potential measurement, per a method 440, a system (e.g., such as the
ENSITE® NAVX® system) delivers low level separable currents from
the three substantially orthogonal electrode pairs (422, 422', 424, 424',
426, 426') positioned on the body surface (delivery block 442) and
optionally the electrode 428 (or one or more other electrodes). The
specific position of a catheter (or lead) electrode within a chamber of
the heart can then be established based on three resulting potentials
measured between the recording electrode with respect to a reference
electrode, as seen over the distance from each patch set to the recording
tip electrode (measurement block 444). Sequential positioning of a
catheter (or lead) at multiple sites along the endocardial surface of a
specific chamber can establish that chamber's geometry, i.e., position
mapping (position/motion mapping block 446). Where the catheter (or lead)
430 moves, the method 440 may also measure motion.

[0097] In addition to mapping at specific points, the ENSITE®
NAVX® system provides for interpolation (mapping a smooth surface)
onto which activation voltages and times can be registered. Around 50
points are required to establish a surface geometry and activation of a
chamber at an appropriate resolution. The ENSITE® NAVX® system
also permits the simultaneous display of multiple catheter electrode
sites, and also reflects real-time motion of both ablation catheters and
those positioned elsewhere in the heart.

[0098] The ENSITE® NAVX® system relies on catheters for temporary
placement in the body. Various exemplary techniques described herein
optionally use one or more electrodes for chronic implantation. Such
electrodes may be associated with a lead, an implantable device, or other
chronically implantable component. Referring again to FIG. 3, the
configuration block 310 indicates that intraoperative configurations 312
and chronic configurations 314 may be available. Intraoperative
configurations 312 may rely on a catheter and/or a lead suitable for
chronic implantation.

[0099] With respect to motion, the exemplary system and method 400 may
track motion of an electrode in one or more dimensions. For example, a
plot 450 of motion versus time for three dimensions corresponds to motion
of one or more electrodes of the catheter (or lead) 430 positioned in a
vessel 103 of the heart 102 where the catheter (or lead) 430 includes the
one or more electrodes 432, 432'. Two arrows indicate possible motion of
the catheter (or lead) 430 where hysteresis may occur over a cardiac
cycle. For example, a systolic path may differ from a diastolic path. An
exemplary method may analyze hysteresis for any of a variety of purposes
including selection of a stimulation site, selection of a sensing site,
diagnosis of cardiac condition, etc.

[0100] The exemplary method 440, as mentioned, includes the delivery block
442 for delivery of current, the measurement block 444 to measure
potential in a field defined by the delivered current and the mapping
block 446 to map motion based at least in part on the measured potential.
According to such a method, motion during systole and/or diastole may be
associated with electrical information. Alone, or in combination with
electrical information, the mechanical motion information may be used for
selection of optimal stimulation site(s), determination of hemodynamic
surrogates (e.g., surrogates to stroke volume, contractility, etc.),
optimization of CRT, placement of leads, determination of pacing
parameters (AV delay, VV delay, etc.), etc.

[0101] The system 400 may use one or more features of the aforementioned
ENSITE® NAVX® system. For example, one or more pairs of
electrodes (422, 422', 424, 424', 426, 426') may be used to define one or
more dimensions by delivering an electrical signal or signals to a body
and/or by sensing an electrical signal or signals. Such electrodes (e.g.,
patch electrodes) may be used in conjunction with one or more electrodes
positioned in the body (e.g., the electrodes 432, 432').

[0102] The exemplary system 400 may be used to track motion of one or more
electrodes due to systolic motion, diastolic motion, respiratory motion,
etc. Electrodes may be positioned along the endocardium and/or epicardium
during a scouting or mapping process for use in conjunction with
electrical information. Such information may also be used alone, or in
conjunction with electrical information, for identifying the optimal
location of an electrode or electrodes for use in delivering CRT. For
example, a location may be selected for optimal stimulation, for optimal
sensing, or other purposes (e.g., anchoring ability, etc.).

[0103] With respect to stimulation, stimulation may be delivered to
control cardiac mechanics (e.g., contraction of a chamber of the heart)
and motion information may be acquired where the motion information is
associated with the controlled cardiac mechanics. An exemplary selection
process may identify the best stimulation site based on factors such as
electrical activity, electromechanical delay, extent of motion,
synchronicity of motion where motion may be classified as systolic motion
or diastolic motion. In general, motion information corresponds to motion
of an electrode or electrodes (e.g., endocardial electrodes, epicardial
electrodes, etc.) and may be related to motion of the heart.

[0104] FIG. 5 shows a field compensation scheme 500 for a localization
system. As mentioned, the ENSITE® NAVX® system includes a feature
known as "field scaling", which may operate according to the scheme 500.
As described herein, exemplary electrodes can enhance mapping of field
heterogeneities and increase accuracy of position determinations (e.g.,
via compensation techniques).

[0105] A diagram of field heterogeneity 510 shows a cross-section between
the Y-axis patches 424, 424'. Internal physiology and accompanying
dielectric properties introduce field heterogeneities. Further, as
physiology changes with respect to time due to cardiac function,
respiration, patient position, etc., heterogeneities vary with respect to
time as well.

[0106] An exemplary compensation method 560 commences in a positioning
block 562 that positions at least two electrodes. A measurement block 564
measures potential for each of the electrodes. A comparison block 566
follows that includes measuring or otherwise providing for a distance or
angle between the at least two electrodes. For example, an electrode may
be considered a fiducial and spacing between two or more electrodes known
a priori. In an alternative example, a lead may have fiducials with known
spacing that are visible via x-ray imaging along with the electrodes. In
such an example, a clinician may simply count the number of fiducials
between electrodes. In yet another example, one or more anatomical
features may be relied upon to establish a distance that can be used to
infer a distance between two electrodes. Of course, combinations of such
techniques may be used.

[0107] According to the method 560, a determination block 568 determines
whether and to what extent the field is heterogeneous. For example, if a
known distance between two electrodes is 5 mm and the current generated
field is expected to have a particular field gradient over a distance of
5 mm, then the potentials can be analyzed to determine if the field
gradient differs from its expected field gradient. Given an appropriate
number of determinations, a generation block 570 generates a field
compensation transform, algorithm, map, table or the like. The method 560
then proceeds to an acquisition block 572 that acquires potentials and
compensates accordingly for field heterogeneities to provide more
accurate position information.

[0108] When a localization system is configured to define one or more
electrodes as belonging to a single lead or catheter, such a system may
display a "tube" that represents the lead body between two electrodes. In
the ENSITE® NAVX® system, this display, however, is simply
graphical and represented as a straight line, a polynomial, or a spline.
As such, it does not truly represent the trajectory or orientation of a
lead body in the heart.

[0109] As described herein, various exemplary electrodes allow for
determination of trajectory or orientation of an electrode, an electrode
array, a lead body or a portion of a lead body. Such electrodes can allow
a localization system to determine not only the position of an electrode
but also its orientation, which can enhance the representation of a lead,
enhance computed parameters related to the motion of an electrode or
lead, etc.

[0110] FIG. 6 shows an exemplary two lead scenario 600 along with local
coordinate systems for each of the leads 610, 630. In the example of FIG.
6, electrodes on the leads 610, 630 are conventional ring electrodes,
which fail to yield rich positional information in the local coordinate
systems.

[0111] In FIG. 6, the two local coordinate systems (x, y, z and x', y', z'
dimensions) are shown along with a global coordinate system (X, Y, Z
dimensions). While Cartesian coordinates are shown in the example of FIG.
6, other coordinate systems may be utilized.

[0112] The leads 610, 630 include two electrodes defined with respect to a
z-axis: z(n) and z(n-1) with a separation of Δz. In the local
coordinate systems, the leads 610, 630 may yaw, pitch or roll. Yaw
involves rotation about the y-axis, pitch involves rotation about the
x-axis and roll involves rotation about the z-axis.

[0113] If the lead is viewed as a vehicle in the body, yaw is lateral
rotational or oscillatory movement of the vehicle about its vertical
axis. Given this vehicle analogy, pitch is movement about an axis that is
perpendicular to the vehicle's longitudinal axis and horizontal with
respect to its primary body. Pitch attitude is the orientation of the
vehicle with respect to the pitch axis. The pitching moment is the rising
and falling of the vehicle's nose. When the nose rises, the pitching
moment is positive; when the nose drops, the pitching moment is negative
and is also called a diving moment. As for roll, it represents motion of
the vehicle about its longitudinal, or nose-tail, axis.

[0114] The exemplary local coordinate systems approach of FIG. 6 can
assist in navigation of a lead in a patient's body. Further, an analogy
to vehicle motion facilitates implementation of automated or assisted
navigation control (e.g., 3-D robotic control in conjunction with a
localization system).

[0115] As mentioned, the ring electrodes, having a symmetric axis or
rotation about the z-axis cannot readily provide for orientation of the
lead 610 or the lead 630. To demonstrate this point, FIG. 7 shows a
diagram of a conventional lead with symmetric roll 710 and an exemplary
lead with asymmetric roll 720 as well as an exemplary method 750 for
using the lead 720. The exemplary lead 720 includes two electrodes that
are shaped and positioned like opposing boiler plates but offset along
the z-axis. Further, the electrical center of each electrode is offset
from the z-axis (e.g., as shown, +/-x-axis). Thus, lead roll causes the
electrical centers of the electrodes to move in the x,y-plane, which,
given a surrounding field of a localization system, will result in
changing positions of the two electrodes (see, e.g., electrical centers
in example 930 of FIG. 9).

[0116] The exemplary method 750 includes a positioning block 752 where a
clinician positions a lead such as the lead 720 in a patient's body. For
example, the clinician may position a lead in a patient where the lead
has a longitudinal axis that extends from a proximal end to a distal end
and where the lead includes an electrode with an electrical center offset
from the longitudinal axis of the lead body. After or during positioning,
in a measurement block 754, the clinician instructs a localization system
to measure electrical potential in a three-dimensional potential field
using the electrode. In a determination block 756, a localization system
determines, based on measured electrical potential and the offset of the
electrical center, lead roll about the longitudinal axis of the lead body
(e.g., in degrees, radians, etc.). As described herein, an exemplary
method can include displaying a lead roll indicator on a display, for
example, where the lead roll indicator indicates degrees of roll about a
longitudinal axis of a lead body. Such a method may include positioning
an electrode of a lead based at least in part on the determined lead roll
(e.g., to be directed toward or away from tissue such as nerve tissue,
damaged myocardium, etc.).

[0117] FIG. 8 shows an exemplary lead 800 with twist tracking features as
well as an exemplary method 850 for determining twist. The lead 800
includes a distal pair of electrodes 820 and a proximal pair of
electrodes 840. As the lead 800 is resilient, its body may twist such
that a roll differential exists between the distal pair 820 and the
proximal pair 840. In this example, two local coordinate systems may be
defined, one for each of the electrode pairs 820, 840. Even where the
lead 800 remains at a particular point in the body (e.g. tip position),
rotation or twist may be tracked with respect to a clinician's actions or
with respect to body actions or function.

[0118] The exemplary method 850 includes a positioning block 852 where a
clinician positions a lead such as the lead 800 in a patient's body. For
example, the clinician may position a lead in a patient where the lead
has a longitudinal axis that extends from a proximal end to a distal end
and where the lead includes electrodes where at least two electrodes have
an electrical center offset from the longitudinal axis of the lead body.
After or during positioning, in a measurement block 854, the clinician
instructs a localization system to measure electrical potential in a
three-dimensional potential field using the at least two electrodes. In a
determination block 856, a localization system determines, based on
measured electrical potential and the offsets of the electrical centers,
local lead roll and lead twist about the longitudinal axis of the lead
body (e.g., in degrees, radians, etc.).

[0119] FIG. 9 shows various views of a conventional ring electrode 910 and
an exemplary pair of electrodes 930. These views further demonstrate how
electrical centers vary or do not vary with respect to electrode
characteristics. As shown, the conventional ring electrode 910 has an
electrical center along a central axis of rotation. A view along this
axis shows the electrical center of the ring electrode 910 centered such
that rotation about the axis does not result in displacement of Its
electrical center from the axis. Further, rotation of the ring electrode
910 about its geometric center does not result in displacement of its
electrical center.

[0120] In contrast, each of the individual electrodes of the pair 930 has
an electrical center offset from a central axis (e.g., z-axis). A view
along this axis shows the two distinct electrical centers. Further
rotation about the geometric center of the pair of electrodes 930 results
in displacement of each electrical center.

[0121] Given the foregoing discussion of coordinate systems and electrical
centers, various exemplary electrodes are shown in FIGS. 10 and 11 as
being part of a lead. Specifically, FIG. 10 shows exemplary electrode
configurations 1010, 1020, and 1030 and FIG. 11 shows exemplary electrode
configurations 1040 and 1050. Such arrangements may include one or more
circuits such as the circuit 168 of the lead 160 of FIG. 1 (e.g., to
select or otherwise control an electrode configuration).

[0122] The configuration 1010 includes a lead body 1012 and two series of
electrodes 1014, 1016 where each series includes individually selectable
ring electrodes 1018. Each of the series of electrodes 1014, 1016 may be
formed by splitting, perpendicular to the lead body axis, a single
electrode such that it resembles two or more rings arranged end-to-end
lengthwise.

[0123] The configuration 1010 may be used as a marquee whereby a
localization system successively displays a position for each individual
ring in a series. Thus, the display would appear as a moving sequence of
dots or the like progressing along the axis of the lead body 1012 (e.g.,
a successive series of markers). When the direction is known (e.g., from
proximal to distal), a clinician can readily ascertain the orientation of
the lead body 1012. Further, the localization system may display colors
or other indicia to indicate a corresponding direction (e.g., vector).
For example, a red vector may indicate a direction "into" a display pane
(e.g., away from an observer) while a blue vector may indicate a
direction "out of" a display pane (e.g., toward an observer). Yet
further, where the series 1014, 1016 are spaced at some distance, the
localization system may display colors or other indicia to same or
opposing directions. As described herein, an exemplary method may include
altering a color of the lead direction marquee, for example, based on
direction of the lead direction marquee with respect to a coordinate
system (e.g., a coordinate system that corresponds to physiology of the
heart, a patient's body, etc.).

[0124] The configuration 1020 includes a lead body 1022 and two series of
electrodes 1024, 1026 where each series includes individually selectable
arc section electrodes 1028. Each of the series of electrodes 1024, 1026
may be formed by splitting a single electrode such that it resembles two
or more arced sections arranged circumferentially. For example, the lead
160 of FIG. 1 includes electrodes 163, which are arranged
circumferentially about a lead body. As mentioned, various exemplary
leads may include one or more circuits for control of one or more
electrodes in an electrode array (see, e.g., the circuit 168 of the lead
160 of FIG. 1).

[0125] The configuration 1030 includes a lead body 1032 and two sets of
electrodes 1034, 1036 where each set includes individually selectable
cylindrical section electrodes 1038. Each set of electrodes 1034, 1036
may be formed by splitting a single electrode such that it resembles two
cylindrical sections with an axial offset along the split boundary. Such
an electrode set was described with respect to FIG. 9 (see electrodes
930), specifically to explain electrical centers. As shown in FIG. 10,
each set has circumferential and axial features. In a particular example,
each set 1034, 1036 can include two or more interlocking pieces that can
form a complete ring, which may be referred to as an interlocking
arrangement.

[0126] The configuration 1040 includes a lead body 1042 and two sets of
electrodes 1044, 1046 where each set includes individually or group
selectable electrodes 1048 arranged circumferentially. Each set of
electrodes 1044, 1046 is optionally formed by a group of conductors where
each conductor is attached to or forms an exposed end surface along the
lead body 1042 arranged circumferentially that, when taken together,
resemble a ring. In FIG. 11, the configuration 1040 may be referred to as
a tiled arrangement.

[0127] The configuration 1050 includes a lead body 1052 and two sets of
electrodes 1054, 1056 where each set includes individually or group
selectable electrodes 1058 arranged circumferentially and axially in a
helix or spiral fashion. Each set of electrodes 1054, 1056 is optionally
formed by a group of conductors where each conductor is attached to or
forms an exposed end surface along the lead body 1052 arranged
circumferentially and axially that, when taken together, resemble a ring.
In FIG. 11, the configuration 1050 may be referred to as a spiral
arrangement.

[0128] In the examples of FIGS. 10 and 11, the electrode sets may be
(e.g., for purposes of cardiac study and therapy), approximately 0.3 mm
to approximately 4.0 mm in diameter and approximately 0.5 mm to
approximately 2.5 mm in length.

[0129] FIG. 12 shows exemplary electrodes configurations 1210, 1220, which
are suitable for determination of local field heterogeneities. The
configurations 1210, 1220 include one or more split-ring electrodes. As
described herein, a circumferential arrangement or a combination of
circumferential and axial arrangements are particularly suited to
determining local field heterogeneities.

[0130] The configuration 1210 includes a lead body 1212 and two sets of
electrodes 1214, 1216 where each set includes individually or group
selectable electrodes arranged circumferentially and axially. Each set of
electrodes 1214, 1216 has one or more associated conductors for
electrodes of proximal, middle, and distal portions. In the example of
FIG. 12, the proximal and distal portions cover the complete
circumference of the lead body 1212 and the middle portion (e.g., portion
1218) is subdivided into three or more portions about the circumference
of the lead body 1212.

[0131] The configuration 1220 includes a lead body 1222 and two sets of
electrodes 1224, 1226 where each set includes individually or group
selectable electrodes arranged circumferentially and axially. Each set of
electrodes 1224, 1226 has one or more associated conductors for
electrodes of proximal and distal portions. In the example of FIG. 12,
the proximal and distal portions are subdivided in two or more
circumferential portions that are staggered with respect to one another
(see, e.g., cross-section of electrode 1228).

[0132] As described herein, since distance between electrode portions in
each direction in local lead or catheter coordinates is known and
typically fixed, the corresponding distance measured in localization
system coordinates (e.g., ENSITE® NAVX® system 3D field
coordinates) can be used to define a local field scaling factor.

[0133] FIG. 13 shows various exemplary methods and displays using a
localization system 1300. The heart 102 is shown with a right ventricular
lead 1308 and a left ventricular lead 1306 with a guidance catheter 1315.
The right ventricular lead 1308 includes a pair of electrodes 1330 having
electrical centers offset from a longitudinal axis of the lead body and a
tip electrode with a screw or helix 1328 for attachment to the
myocardium. The left ventricular lead includes a series of electrodes
1323 with a combination of marquee electrodes (see, e.g., electrodes 1010
of FIG. 10) and interlocking electrodes (see, e.g., electrodes 1030 of
FIG. 10).

[0134] In the example of FIG. 13, a catheter or sheath 1315 is used for
placement of the left ventricular lead 1306. The catheter 1315 includes a
pair of electrodes 1317 having electrical centers offset from a
longitudinal axis of the catheter 1315.

[0135] A localization system 1380 is configured via a switching module
1384 to acquire information from the various electrodes, configured via a
compensation module 1386 to compensate for field heterogeneity and
configured via a display module 1388 to generate data suitable for
display on a monitor, screen, etc. As described herein, a localization
system may include an integral display (e.g., as part of a console or
notebook like arrangement) or may include memory to store data suitable
for display (e.g., in a graphics buffer). A localization system typically
includes one or more graphics processors (e.g., a graphics accelerator
card, display adapter, etc.) configured for generating multidimensional
graphics data that can be rendered on a display for viewing by a
clinician. Communication between a localization system and a display may
occur via wire or wirelessly or via a combination of both wire and
wireless communication. Data may also be stored to a storage device and
then loaded to a system for display. The display module 1388 includes
software or hardware and software for generating data suitable for
display on a monitor, screen, etc.

[0136] An exemplary RV lead display 1392 based on data generated by the
display module 1388 shows a graphic of electrical centers of the
electrodes 1330 with respect to the tip electrode screw 1328. Insertion
of the tip electrode screw 1328 may be achieved in any of a variety of
manners. For example, a stylet may be inserted in a lumen of the RV lead
1308 and rotated to rotate the tip electrode screw 1328 (e.g., clockwise,
counter-clockwise or both clockwise and counter-clockwise). In such an
example, the electrodes 1330 may be tracked to determine if the RV lead
1308 is rotating as the stylet is rotated. Further, the localization
system 1380 may track the axial distance (e.g., in a local coordinate
system) between the electrodes 1330 and the tip electrode screw 1328 as
the tip electrode screw 1328 is inserted into the myocardium. The display
1392 may indicate the axial distance as a displacement that a clinician
may track during an implant procedure.

[0137] An exemplary sheath display 1394 based on data generated by the
display module 1388 shows an angle of rotation offset between the
catheter or sheath 1315 and the LV lead 1306. The display 1394 also shows
an outline of the ostium of the coronary sinus as an anatomical reference
for a clinician. In such an example, a clinician may seek to avoid
binding of the LV lead 1306 in the sheath 1315 as the LV lead 1306 is
positioned in a vein. Such a display can track total rotation (e.g.,
beyond 360 degrees) and account for positive and negative rotation
whether stemming from the sheath 1315 or the LV lead 1306. In the example
of FIG. 13, the rotation of the LV lead 1306 may be inferred by
information acquired via the series of electrodes 1323 or other
electrodes or proximal end information (e.g., an end manipulated by a
clinician) or a combination of such aforementioned information.

[0138] An exemplary LV lead display 1396 based on data generated by the
display module 1388 shows a marquee for the series of electrodes 1323
along with a rotation graphic. In combination, a clinician can readily
ascertain direction and orientation of the distal portion of the lead
1306. In the example of FIG. 13, the display 1396 includes a marquee
speed indicator, which may correspond to a sampling speed for all or
certain electrodes of the series 1323. The localization system 1380 may
be configured to receive input from a clinician to control the marquee
speed, which can facilitate placement of a lead (e.g., to coordinate with
speed or timing of a clinician's hand or control movements).

[0139] In the example of FIG. 13, the display 1396 pertains to navigating
a lead in a secondary or tertiary branch of the coronary venous system
(e.g., tributaries to the coronary sinus). As described herein, the
exemplary display 1396 may be applied for display of orientation of a
lead or catheter tip, for example, while delivering an active fixation
lead or while ablating cardiac or other tissue.

[0140] As described herein, an exemplary method can acquire position
information using an exemplary lead and determine instantaneous tangent
direction along the lead. Such information may be used to accurately
render representations of lead bodies on a localization system monitor.
In various situations, instantaneous tangent direction along a lead body
may be used to determine local myocardial performance (e.g., for CRT
optimization).

[0141] With respect to a lead that includes a helix (e.g., as an anchoring
screw or mechanism), a keyed-tip stylet or a "helix extender" tool (e.g.,
a piece that clips onto proximal pin and rotates) may be used to deploy a
helix without rotating a lead. Alternatively, a lead could be rotated if
a helix portion were already extended, for example, to screw a fixed
helix into tissue. Various active-fixation leads include a helix that can
extend and retract. An exemplary arrangement can include a lead body with
an electrode having an electrical center offset from the longitudinal
axis of the lead body, which would allow for determinations as to
orientation of the lead body. An exemplary arrangement may include a
marquee array to determine how far a helix has been extended (e.g., where
the further the helix is extended, the more distal the electrical center
has moved from another electrode on a known location near the distal
portion of the lead, for example, an active "mapping collar"). For a
helix that rotates, either independently during deployment or as part of
the overall lead rotation of a fixed-helix lead, an exemplary arrangement
may allow for an electrical center of the helix to be slightly offset
from the longitudinal axis due to the fact that the most distal "turn" of
the helix comes to a point and does not complete 360 degrees. While such
a offset of an electrical center may be small, a localization system may
have sufficient resolution and accuracy to distinguish the offset (e.g.,
optionally differentially with respect to from a full cylindrical
marker).

[0142] FIG. 14 shows an exemplary localization system 1400, an exemplary
method 1470 and an exemplary data entry sequence 1490. The localization
system 1400 includes an electrode/lead reference information module 1410,
a switching module 1430 and a display module 1450. The module 1410 may
access one or more databases that contain information as to electrodes,
leads, combinations of leads and electrodes suitable for use with
features of the localization system 1400.

[0143] Specifically, the localization system 1400 may access information
about a lead and determine, based on characteristics of the lead, how the
lead may be used with respect to various hardware, software or hardware
and software features of the localization system 1400. The module 1410
may include instructions to identify a lead and its electrode type or
types upon connection to the localization system 1400. Such a process may
be referred to as lead or electrode discovery and can rely on information
such as impedance, resistance, number of conductors, a lead's built in
circuitry (e.g., an ASIC), etc.

[0144] In the example of FIG. 14, the switching module 1430 provides
various types of switching schemes, which may be suited to particular
characteristics of a lead or electrodes, including the type of clinical
procedure. For example, as described with respect to FIG. 13, a screw in
procedure for anchoring a lead (see, e.g., RV lead display 1392) is
different than a navigation procedure (see, e.g., LV lead display 1396).
Thus, the switching module 1430 may include a table or other data
structure or algorithm that associates various factors to present
suitable switching schemes for user selection. Alternatively, the
switching module 1430 may automatically select a switching scheme given
information about a lead and its electrodes.

[0145] The display module 1450 includes various algorithms for generating
data suitable for display. In the example of FIG. 14, the localization
system 1400 may select a display algorithm based on a selected switching
scheme. For example, given a switching scheme for anchoring, the display
module 1450 may select an algorithm that generates data for display of a
myocardial boundary and a screw. As position information is acquired, the
module 1450 may update the location and rotational position of the screw
with respect to the myocardial boundary.

[0146] The exemplary method 1470 may be implemented using a localization
system with the modules 1430 and 1450. The method 1470 commences in an
entry block 1472 where electrode/lead information is entered, for
example, per the various manners discussed above. In a particular
example, a clinician may enter such information via an input device
(e.g., keyboard, touch screen, microphone, mouse, etc.). In a selection
block 1474, a clinician selects an appropriate switching scheme from one
or more available switching schemes. In another selection block 1476, the
clinician selects an appropriate display scheme from one or more
available display schemes. The order of the blocks 1474 and 1476 may be
reversed or may occur simultaneously (e.g., where display infers
switching or where switching infers display).

[0147] Once appropriate information has been entered and selections made,
the method 1470, in an acquisition block 1478, acquires potentials using
the electrodes according to the selected switching scheme. A generation
block 1480 follows that generates data based on the acquired potentials
according to the selected display scheme. Upon display of the data, along
with corresponding graphics, in an action block 1482, a clinician may
take appropriate actions. For example, a clinician may navigate the lead,
anchor a lead, conduct tests, etc.

[0148] The exemplary data entry sequence 1490 demonstrates how and the
type of information a clinician may enter while using a localization
system operating according to the method 1470. In first entry block 1492,
a clinician enters information to notify the localization system that a
series of marquee electrodes will be used on a LV lead. In a second entry
block 1494, the clinician selects a switching scheme for four marquee
electrodes. In a third entry block 1496, the clinician selects a display
scheme that will display the marquee with an electrode-to-electrode
frequency of 20 Hz (e.g., marquee display rate) and with blue and red
vectors or colors to indicate whether the marquee is "pointing" out of
the display screen or into the display screen.

[0149] As described herein, switching may not be required depending on how
electrodes of a lead are configuration for electrical connection to a
localization system. Further, an exemplary lead may include a data
acquisition system and communication system that can communicate acquired
data via a data bus, which may be wired or wireless. For example, a lead
may include a head-end (e.g., proximal end) A/D, data buffer and
communication circuit that can communicate acquired potential data to a
localization system. In such an example, the localization system merely
receives the data and displays the data according to an appropriate
display scheme.

[0150] In various examples, a connection scheme exists where electrodes of
a lead are electrically connected via one or more conductors to a
localization system. For example, a particular arrangement may include
independent conductors connected to each portion of a split-ring
electrode where each of the conductors is connected to a separate channel
of a localization system.

[0151] A localization system can include a module for setup where an
electrode arrangement is defined as axial, circumferential, interlocking,
tiled, etc. and position of any composite electrode (e.g., ring, spiral
or other) may be optionally computed and displayed as an average of each
of its constituent electrode portions. Enhanced tracking features may be
computed by a module by combining appropriate signals in sequence.

[0152] In another exemplary connection scheme, each portion of a
split-ring electrode arrangement has an independent conductor, each of
which is connected to a multiplexing unit (MUX), the output of which
connects to a single channel of a localization system. The multiplexing
unit may (e.g., via software, hardware or hardware and software) combine
various electrodes or electrode portions and transmit one or more
resultant signals to a localization system. In such a scheme, signals
transmitted to the localization system may be perceived as only a single
electrode (e.g., where some form of enhanced tracking has already been
embedded by the multiplexing unit).

[0153] In another exemplary connection scheme, portions of a split-ring
electrode arrangement are connected distally by a chip (e.g., chip-based
circuitry such as an ASIC) that performs the multiplexing and a single
conductor carries the signal to a connection with the localization
system. In this example, the chip carries out the switching scheme, as
appropriate, for desired enhanced localization functionality.

[0154] In another exemplary connection scheme, all portions of a
split-ring electrode arrangement are connected to terminals of a
multi-terminal hardware switch such as a reed switch or some other
electrically, magnetically, or mechanically activated switch. In such an
arrangement, an additional patch or other device connected to a
localization system can activate the switch sequentially to achieve the
desired enhanced function.

[0155] With respect to exemplary switching schemes, a scheme can be
programmed to constantly track a distal-most electrode of an arrangement
of electrodes and sequentially join (e.g., in series) other electrodes of
the arrangement, one or more at a time, from proximal to distal. For
example, in an axial arrangement containing five electrodes, where the
most distal electrode is denoted "A" and the most proximal electrode is
denoted "E", a switching scheme may select the following electrode
combinations: "AE-AD-AC-AB-AE-AD-AC-AB . . . " Alternatively, the most
distal need not always be switched on, but rather simply switch
sequentially from most proximal to most distal, for example:
"E-D-C-B-A-E-D-C-B-A . . . " Alternatively, the distal electrode may be
always switched on, and the scheme programmed to simply turn one or more
proximal electrodes on and off sequentially, for example: "AB-A-AB-A-AB-A
. . . " Such a scheme generates an effect of moving the "center of
gravity" of the electrode arrangement from proximal to distal.
Information acquired according to such a scheme may be displayed on a
monitor as an electrode travelling slightly from proximal to distal along
the axial direction (e.g., a marquee effect).

[0156] Various exemplary schemes can with electrodes at or near the distal
end of a lead can distinguish whether the distal end is pointed
tangential or perpendicular to the heart surface, for example, where a
localization system is used to fix a lead at a particular location (such
as HIS bundle). Further, such a scheme can determine which direction a
lead or catheter is pointed as it reaches a branch point in the coronary
venous system. With respect to pacing therapies, such an approach can aid
sub-branch selection in placement of a pacing lead.

[0157] An exemplary scheme can track electrodes of a lead that are located
along a lead body (e.g., at a distance from a distal end of more than a
centimeter) to more accurately determine the trajectory of the lead body.
For example, based on direction that an electrode is pointing, a
localization system can use not only the position but also tangent
direction in a polynomial or spline calculation to draw a representation
of the lead body. An exemplary method can track changes in direction
throughout a cardiac cycle to yield valuable information about cardiac
rotation. Such information may be used for CRT optimization.

[0158] Various exemplary techniques described herein may be applied to
scenarios where other types of imaging leads or catheters are used (e.g.,
fiber-optic, ultrasound, or other modalities). For example, in such a
scenario, a localization system can acquire information and determine
what direction an imaging lead is pointing, which can help to optimize
image acquisition. Such techniques can aid imaging modalities that rely
on Doppler methods or backscatter, especially those that may require
parallel or perpendicular orientations for the most accurate results.

[0159] As described herein, various exemplary electrodes may be used to
determine local deformation gradient. For example, a circumferential or
interlocking arrangement may be used with an independent-channel
connection to a localization system to acquire information for
observation of motion as to local deformation. In contrast, for a single,
solid electrode, only the extent of average motion in the (x,y,z)
Cartesian field can be determined. By observing differential motion of
each portion of an exemplary electrode arrangement, not only (x,y,z)
components but also rotation about the lead axis and tilt of the catheter
axis can be determined. Such detailed motion information can be plugged
into a deformation tensor computed for tissue next to the electrode
arrangement, yielding valuable information about the local tissue
mechanical performance. Such information can be used in conjunction with
various CRT optimization schemes.

Exemplary External Programmer

[0160] FIG. 15 illustrates pertinent components of an external programmer
1500 for use in programming an implantable medical device 100 (see, e.g.,
FIGS. 1 and 2). The external programmer 1500 optionally receives
information from other diagnostic equipment 1650, which may be a
computing device capable of acquiring motion information related to
cardiac mechanics. For example, the equipment 1650 may include a
computing device to deliver current and to measure potentials using a
variety of electrodes including at least one electrode positionable in
the body (e.g., in a vessel, in a chamber of the heart, within the
pericardium, etc.). Equipment may include a lead for chronic implantation
or a catheter for temporary implantation in a patient's body. Equipment
may allow for acquisition of respiratory motion and aid the programmer
1500 in distinguishing respiratory motion from cardiac.

[0161] Briefly, the programmer 1500 permits a clinician or other user to
program the operation of the implanted device 100 and to retrieve and
display information received from the implanted device 100 such as IEGM
data and device diagnostic data. The programmer 1500 may also instruct a
device or diagnostic equipment to deliver current to generate one or more
potential fields within a patient's body where the implantable device 100
may be capable of measuring potentials associated with the field(s).

[0162] The external programmer 1500 may be configured to receive and
display ECG data from separate external ECG leads 1732 that may be
attached to the patient. The programmer 1500 optionally receives ECG
information from an ECG unit external to the programmer 1500. The
programmer 1500 may use techniques to account for respiration.

[0163] Depending upon the specific programming, the external programmer
1500 may also be capable of processing and analyzing data received from
the implanted device 100 and from ECG leads 1732 to, for example, render
diagnosis as to medical conditions of the patient or to the operations of
the implanted device 100. As noted, the programmer 1500 is also
configured to receive data representative of conduction time delays from
the atria to the ventricles and to determine, therefrom, an optimal or
preferred configuration for pacing. Further, the programmer 1500 may
receive information such as ECG information, IEGM information,
information from diagnostic equipment, etc., and determine one or more
metrics for optimizing therapy.

[0164] Considering the components of programmer 1500, operations of the
programmer are controlled by a CPU 1702, which may be a generally
programmable microprocessor or microcontroller or may be a dedicated
processing device such as an application specific integrated circuit
(ASIC) or the like. Software instructions to be performed by the CPU are
accessed via an internal bus 1704 from a read only memory (ROM) 1706 and
random access memory 1730. Additional software may be accessed from a
hard drive 1708, floppy drive 1710, and CD ROM drive 1712, or other
suitable permanent or removable mass storage device. Depending upon the
specific implementation, a basic input output system (BIOS) is retrieved
from the ROM 1706 by CPU 1702 at power up. Based upon instructions
provided in the BIOS, the CPU 1702 "boots up" the overall system in
accordance with well-established computer processing techniques.

[0165] Once operating, the CPU 1702 displays a menu of programming options
to the user via an LCD display 1614 or other suitable computer display
device. To this end, the CPU 1702 may, for example, display a menu of
specific programming parameters of the implanted device 100 to be
programmed or may display a menu of types of diagnostic data to be
retrieved and displayed. In response thereto, the clinician enters
various commands via either a touch screen 1616 overlaid on the LCD
display or through a standard keyboard 1618 supplemented by additional
custom keys 1620, such as an emergency VVI (EVVI) key. The EVVI key sets
the implanted device to a safe WI mode with high pacing outputs. This
ensures life sustaining pacing operation in nearly all situations but by
no means is it desirable to leave the implantable device in the EVVI mode
at all times.

[0166] With regard to mapping of metrics (e.g., for patterns of
conduction), the CPU 1702 includes a 3-D mapping system 1747 and an
associated data analysis system 1749. The systems 1747 and 1749 may
receive position information and physiological information from the
implantable device 100 and/or diagnostic equipment 1650. The data
analysis system 1749 optionally includes control logic to associate
information and to make one or more conclusions based on metrics, for
example, as indicated in FIG. 3 to optimize delivery of therapy (e.g., to
optimize a pacing configuration).

[0167] Where information is received from the implanted device 100, a
telemetry wand 1728 may be used. Other forms of wireless communication
exist as well as forms of communication where the body is used as a
"wire" to communicate information from the implantable device 100 to the
programmer 1500.

[0168] If information is received directly from diagnostic equipment 1650,
any appropriate input may be used, such as parallel 10 circuit 1740 or
serial 10 circuit 1742. Motion information received via the device 100 or
via other diagnostic equipment 1650 may be analyzed using the mapping
system 1747. In particular, the mapping system 1747 (e.g., control logic)
may identify positions within the body of a patient and associate such
positions with one or more electrodes where such electrodes may be
capable of delivering stimulation energy to the heart, performing other
actions or be associated with one or more sensors.

[0169] A communication interface 1745 optionally allows for wired or
wireless communication with diagnostic equipment 1650 or other equipment
(e.g., equipment to ablate or otherwise treat a patient). The
communication interface 1745 may be a network interface connected to a
network (e.g., intranet, Internet, etc.).

[0170] A map or model of cardiac information may be displayed using
display 1614 based, in part, on 3-D heart information and optionally 3-D
torso information that facilitates interpretation of information. Such
3-D information may be input via ports 1740, 1742, 1745 from, for
example, a database, a 3-D imaging system, a 3-D location digitizing
apparatus (e.g., stereotactic localization system with sensors and/or
probes) capable of digitizing the 3-D location. While 3-D information and
localization are mentioned, information may be provided with fewer
dimensions (e.g., 1-D or 2-D). For example, where motion in one dimension
is insignificant to one or more other dimensions, then fewer dimensions
may be used, which can simplify procedures and reduce computing
requirements of a programmer, an implantable device, etc. The programmer
1500 optionally records procedures and allows for playback (e.g., for
subsequent review). For example, a heart map and all of the electrical
activation data, mechanical activation data, etc., may be recorded for
subsequent review, perhaps if an electrode needs to be repositioned or
one or more other factors need to be changed (e.g., to achieve an optimal
configuration). Electrodes may be lead based or non-lead based, for
example, an implantable device may operate as an electrode and be self
powered and controlled or be in a slave-master relationship with another
implantable device (e.g., consider a satellite pacemaker, etc.). An
implantable device may use one or more epicardial electrodes.

[0171] Once all pacing leads are mounted and all pacing devices are
implanted (e.g., master pacemaker, satellite pacemaker, biventricular
pacemaker), the various devices are optionally further programmed.

[0172] The telemetry subsystem 1722 may include its own separate CPU 1724
for coordinating the operations of the telemetry subsystem. In a dual CPU
system, the main CPU 1702 of programmer communicates with telemetry
subsystem CPU 1724 via internal bus 1704. Telemetry subsystem
additionally includes a telemetry circuit 1726 connected to telemetry
wand 1728, which, in turn, receives and transmits signals
electromagnetically from a telemetry unit of the implanted device. The
telemetry wand is placed over the chest of the patient near the implanted
device 100 to permit reliable transmission of data between the telemetry
wand and the implanted device.

[0173] Typically, at the beginning of the programming session, the
external programming device 1500 controls the implanted device(s) 100 via
appropriate signals generated by the telemetry wand to output all
previously recorded patient and device diagnostic information. Patient
diagnostic information may include, for example, motion information
(e.g., cardiac, respiratory, etc.) recorded IEGM data and statistical
patient data such as the percentage of paced versus sensed heartbeats.
Device diagnostic data includes, for example, information representative
of the operation of the implanted device such as lead impedances, battery
voltages, battery recommended replacement time (RRT) information and the
like.

[0174] Data retrieved from the implanted device(s) 100 can be stored by
external programmer 1500 (e.g., within a random access memory (RAM) 1730,
hard drive 1708, within a floppy diskette placed within floppy drive
1710). Additionally, or in the alternative, data may be permanently or
semi-permanently stored within a compact disk (CD) or other digital media
disk, if the overall system is configured with a drive for recording data
onto digital media disks, such as a write once read many (WORM) drive.
Where the programmer 1500 has a communication link to an external storage
device or network storage device, then information may be stored in such
a manner (e.g., on-site database, off-site database, etc.). The
programmer 1500 optionally receives data from such storage devices.

[0175] A typical procedure may include transferring all patient and device
diagnostic data stored in an implanted device 100 to the programmer 1500.
The implanted device(s) 100 may be further controlled to transmit
additional data in real time as it is detected by the implanted device(s)
100, such as additional motion information, IEGM data, lead impedance
data, and the like. Additionally, or in the alternative, telemetry
subsystem 1722 receives ECG signals from ECG leads 1732 via an ECG
processing circuit 1734. As with data retrieved from the implanted device
100, signals received from the ECG leads are stored within one or more of
the storage devices of the programmer 1500. Typically, ECG leads output
analog electrical signals representative of the ECG. Accordingly, ECG
circuit 1734 includes analog to digital conversion circuitry for
converting the signals to digital data appropriate for further processing
within programmer 1500. Depending upon the implementation, the ECG
circuit 1743 may be configured to convert the analog signals into event
record data for ease of processing along with the event record data
retrieved from the implanted device. Typically, signals received from the
ECG leads 1732 are received and processed in real time.

[0176] Thus, the programmer 1500 is configured to receive data from a
variety of sources such as, but not limited to, the implanted device 100,
the diagnostic equipment 1650 and directly or indirectly via external ECG
leads (e.g., subsystem 1722 or external ECG system). The diagnostic
equipment 1650 includes wired 1654 and/or wireless capabilities 1652
which optionally operate via a network that includes the programmer 1500
and the diagnostic equipment 1650 or data storage associated with the
diagnostic equipment 1650.

[0177] Data retrieved from the implanted device(s) 100 typically includes
parameters representative of the current programming state of the
implanted devices. Under the control of the clinician, the external
programmer displays the current programming parameters and permits the
clinician to reprogram the parameters. To this end, the clinician enters
appropriate commands via any of the aforementioned input devices and,
under control of CPU 1702, the programming commands are converted to
specific programming parameters for transmission to the implanted device
100 via telemetry wand 1728 to thereby reprogram the implanted device 100
or other devices, as appropriate.

[0178] Prior to reprogramming specific parameters, the clinician may
control the external programmer 1500 to display any or all of the data
retrieved from the implanted device 100, from the ECG leads 1732,
including displays of ECGs, IEGMs, statistical patient information (e.g.,
via a database or other source), diagnostic equipment 1650, etc. Any or
all of the information displayed by programmer may also be printed using
a printer 1736.

[0179] A wide variety of parameters may be programmed by a clinician. In
particular, for CRT, the AV delay and the VV delay of the implanted
device(s) 100 are set to optimize cardiac function. In one example, the
VV delay is first set to zero while the AV delay is adjusted to achieve
the best possible cardiac function, optionally based on motion
information. Then, VV delay may be adjusted to achieve still further
enhancements in cardiac function.

[0180] Programmer 1500 optionally includes a modem to permit direct
transmission of data to other programmers via the public switched
telephone network (PSTN) or other interconnection line, such as a T1 line
or fiber optic cable. Depending upon the implementation, the modem may be
connected directly to internal bus 1704 may be connected to the internal
bus via either a parallel port 1740 or a serial port 1742.

[0181] Other peripheral devices may be connected to the external
programmer via the parallel port 1740, the serial port 1742, the
communication interface 1745, etc. Although one of each is shown, a
plurality of input output (IO) ports might be provided. A speaker 1744 is
included for providing audible tones to the user, such as a warning beep
in the event improper input is provided by the clinician. Telemetry
subsystem 1722 additionally includes an analog output circuit 1746 for
controlling the transmission of analog output signals, such as IEGM
signals output to an ECG machine or chart recorder.

[0182] With the programmer 1500 configured as shown, a clinician or other
user operating the external programmer is capable of retrieving,
processing and displaying a wide range of information received from the
ECG leads 1732, from the implanted device 100, the diagnostic equipment
1650, etc., and to reprogram the implanted device 100 or other implanted
devices if needed. The descriptions provided herein with respect to FIG.
15 are intended merely to provide an overview of the operation of
programmer and are not intended to describe in detail every feature of
the hardware and software of the device and is not intended to provide an
exhaustive list of the functions performed by the device 1500. Other
devices, particularly computing devices, may be used.

CONCLUSION

[0183] Although exemplary methods, devices, systems, etc., have been
described in language specific to structural features and/or
methodological acts, it is to be understood that the subject matter
defined in the appended claims is not necessarily limited to the specific
features or acts described. Rather, the specific features and acts are
disclosed as exemplary forms of implementing the claimed methods,
devices, systems, etc.